1. Field of the Invention
The present invention relates to a method for inspecting a bolt heater hole provided for inspecting the soundness of a turbine casing clamping bolt.
2. Description of the Related Art
A hole (bolt heater hole) for heat-drawing the bolt in relation to a temperature at the time of driving a turbine is provided in a turbine casing clamping bolt, and a turbine casing is clamped in a state in which the bolt is heated to be a temperature substantially the same as the temperature at the time of driving the turbine by inserting a heater into the hole.
There is a risk that a crack or the like brought about in the bolt heater hole of such a turbine casing clamping bolt may result in breakage of the bolt. However, because an inspection of a bolt heater hole has not been conventionally required, an inspection technique thereof has not been particularly established.
For example, as a method for inspecting an inner surface of a tube body, a liquid penetrant test (for example, in Jpn. Pat. Appln. KOKAI Publication No. 09-196863) method has been known. In this liquid penetrant test method, a colored liquid or a fluorescent liquid which is generally strongly penetrative is applied onto a surface to be inspected. After the applied liquid is made to sufficiently penetrate into a defect plane of the surface, the penetrant on the surface is removed, the penetrant penetrated into the inner defect is sucked out with a white-micronized developer, and the surface is observed by being illuminated directly or by a black light.
However, when the above-described liquid penetrant test method is applied to an inspection of an inner surface of the bolt heater hole provided in the turbine casing clamping bolt described above, because the bolt heater hole is as small as 20 to 25 mmφ, and is made to be a bottomed and elongated hole, a large-scale device is required in order to automatically carry out a series of processings such as application of a penetrant onto the inner surface of the bolt heater hole, suction of the penetrant by a developer, and the like. Therefore, there is a problem that the structure thereof is complicated, which mounts the costs. Further, because the bolt heater hole has a limited length from the open end to the bottom face unlike a piping, even if an inspection jig is inserted into the bolt heater hole, the apical portion thereof is restricted by the bottom face of the bolt heater hole, making it difficult to apply the processing onto the entire area of the hole surface.